I would think that poi in general is fairly low impact compared to other normal day activities. Definitly very low when compared to any sport or workout activities. I mean, life in general wears you body down, but I'd think poi wouldn't be that bad at all for you. Unless you seriously beat yourself up everytime you spin. Repetitive wise, it's alot less repetitive than sitting in front of a computer typing all day, which is what I get to do here at work:) Poi is at it's most repetitive when you first start out, as you go on it gets alot less as you try out new variations and combos.
I'm sure there are some bad elements to poi, such is life, but I also think the positives greatly outwiegh them.
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Fuzzy Dice.......................................